Device Architecture
2-14 Revision 4
VersaNet Global Networks and Spine Access
The Fusion architecture contains a total of 18 segmented global networks that can access the
VersaTiles, SRAM, and I/O tiles on the Fusion device. There are 6 chip (main) global networks that
access the entire device and 12 quadrant networks (3 in each quadrant). Each device has a total of 18
globals. These VersaNet global networks offer fast, low-skew routing resources for high-fanout nets,
including clock signals. In addition, these highly segmented global networks offer users the flexibility to
create low-skew local networks using spines for up to 180 internal/external clocks (in an AFS1500
device) or other high-fanout nets in Fusion devices. Optimal usage of these low-skew networks can
result in significant improvement in design performance on Fusion devices.
The nine spines available in a vertical column reside in global networks with two separate regions of
scope: the quadrant global network, which has three spines, and the chip (main) global network, which
has six spines. Note that there are three quadrant spines in each quadrant of the device. There are four
quadrant global network regions per device (Figure 2-12 on page 2-13).
The spines are the vertical branches of the global network tree, shown in Figure 2-11 on page 2-12. Each
spine in a vertical column of a chip (main) global network is further divided into two equal-length spine
segments: one in the top and one in the bottom half of the die.
Each spine and its associated ribs cover a certain area of the Fusion device (the "scope" of the spine;
see Figure 2-11 on page 2-12). Each spine is accessed by the dedicated global network MUX tree
architecture, which defines how a particular spine is driven—either by the signal on the global network
from a CCC, for example, or another net defined by the user (Figure 2-13). Quadrant spines can be
driven from user I/Os on the north and south sides of the die, via analog I/Os configured as direct digital
inputs. The ability to drive spines in the quadrant global networks can have a significant effect on system
performance for high-fanout inputs to a design.
Details of the chip (main) global network spine-selection MUX are presented in Figure 2-13. The spine
drivers for each spine are located in the middle of the die.
Quadrant spines are driven from a north or south rib. Access to the top and bottom ribs is from the corner
CCC or from the I/Os on the north and south sides of the device. For details on using spines in Fusion
devices, see the application note Using Global Resources in Actel Fusion Devices.
Figure 2-13 • Spine-Selection MUX of Global Tree
Internal/External
Signal
Internal/External
Signal
Internal/External
Signals
Spine
Global Rib
Global Driver MUX
Tree Node MUX
Tree Node MUX
Internal/External
Signals
Tree Node MUX
